JAK1 and breast cancer: Indeed, Jak1 activation by 5-HT2A/C receptor stimulation has been reported elsewhere48, and this kinase has been shown previously to be associated with STAT3 phosphorylation in mammary cancer cells.49 We confirmed this association in the current work since we also observed an increased STAT3 phosphorylation on MCF-7 cells treated with 5-HT (Fig. 3e, f).